There are many known processes for preparing transparent coating layers for electrostatic, electrophotographic and thermal products. However, most of the known processes involve the use of volatile and toxic solvents, or involve highly unproductive and energy inefficient sputtering or vacuum vapor deposition techniques.
Cuprous iodide is the pigment most often used in preparing ground planes useful for electrostatic and electrophotographic processes. The application of cuprous iodide from solution is disclosed in the article of V. Sumita et al., Journal of Appl. Polymer Science, Vol. 23, pp. 2279-91 (1979). A transparent cuprous iodide layer is obtained by treating polyvinyl alcohol complexes of cupric sulfate with vapors of iodine carried in acetone. The entire process requires special measures to contain the highly toxic iodine vapors and extremely flammable acetone vapors. There are also side reactions which render the system nonconductive and make the process unstable.
The use of acetonitrile or other toxic solvents as a solvent for coating cuprous iodide is disclosed in numerous patents, such as U.S. Pat. No. 3,505,131, and Japanese Patent Publication 58/136044. East German Patent Nos. DD223,550, DD220,155, DD201,527, DD157,369, DD157,368, and DD149,721 illustrate the preparation of conductive layers containing cuprous iodide from organic solutions, including acetonitrile solutions, or the preparation of opaque conductive strips for the purpose of annotation using a dispersion of cuprous iodide in a binder.
Other methods of depositing cuprous iodide are known to the art, e.g., forming complexes of cuprous iodide with alkyl amine compounds. Such processes, however, result in the evolution of complexing ligands during the process of drying the deposited coatings.
Thus, there is a need in the art for a process which can safely and efficiently prepare a more stable dispersion, particularly of cuprous iodide.
In thermal products, the coating components are often encapsulated inside transparent microcapsules, and are used in producing transparent thermal films for printer-plotters and still video camera recording processes. However, the wall of each individual capsule is a heat insulator and thereby provides a barrier for the heat transfer from the thermal head of the printer to the imaging material. Accordingly, circumvention of the need for encapsulation would be beneficial, particularly with respect to the printing density.
There is also a need in the prior art for a process for preparing dispersions useful as transparent conductive layers for electrostatic, electrophotographic and thermal products which permits a high level of purity in the final product. Products which are used in electrostatic, electrophotographic and thermal applications involve functional coatings whose performance often depends on the level of purity involved. Many times, impurities are introduced into the coating via contact with the equipment during the processing of the products.
Accordingly, it is an object of the present invention to provide a process which is capable of producing colloidal dispersions which possess stable physical and chemical characteristics and which can be used in the conductive coating of an electrostatic or electrophotographic imaging element, or in a thermal product.
Yet another objective of the present invention is to provide a process which can produce stable aqueous and solvent based colloidal dispersions.
Still another object of the present invention is to provide a process for preparing thermal products having a transparent coating without the need for encapsulation.
These and other objects of the present invention will become apparent upon a review of the following specification, the Figures of the Drawing, and the claims appended thereto.